In a 1986 study of students who had scored in the top of their age group on either the math or the verbal sections of the S.A.T., the prevalence of left-handers among the high achievers—over fifteen per cent, as compared to the roughly ten percent found in the general population—was higher than in any comparison groups, which included their siblings and parents. Among those who had scored in the top in both the verbal and math sections, the percentage of left-handers jumped to nearly seventeen per cent, for males, and twenty per cent, for females. That advantage echoes an earlier sample of elementary-school children, which found increased left-handedness among children with I.Q. scores above a hundred and thirty-one.

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